NEW YORK — Extensive triple digit heat, broken temperature records and oppressive humidity piled up into a steaming mess as the heat dome crushing the Eastern half of the nation sizzled to what should be its worst Tuesday.

New York City’s John F. Kennedy Airport hit 100 degrees Fahrenheit (38 Celsius) a little after noon, the first time since 2013. Then Baltimore, Philadelphia and Boston joined the 100 club. More than 150 million people woke up to heat warnings and forecasters at the National Weather Service expected dozens of places to tie or set new daily high temperature records Tuesday. The dangerous heat sent people to the hospital, delayed Amtrak trains and caused utilities to urge customers to conserve power.

“Every East Coast state today from Maine to Florida has a chance of 100 degree actual temperature,” said private meteorologist Ryan Maue, a former National Oceanic and Atmospheric Administration chief scientist.

Fryeburg, Maine, also hit 100, for the first time since 2011.

“Getting Maine to 100 degrees is infrequent,” Maue said.

Tuesday’s heat came on top of 39 new or tied heat records Monday. But just as dangerous as triple digit heat is the lack of cooling at night, driven by the humidity.

“You get the combination of the extreme heat and humidity but no relief,” said Jacob Asherman, a meteorologist at NOAA’s Weather Prediction Center. “It’s kind of been just everything stacked on top of itself.... It just speaks to how strong this heat wave is. This is a pretty, pretty extreme event.”

Asherman and Maue said Tuesday is the peak of the high pressure system that sits on top of the Mid-Atlantic and keeps the heat and humidity turned up several notches.

“Nobody is immune to the heat,” said Kimberly McMahon, the weather service public services program manager who specializes in heat and health.

Heat turns dangerous

Dozens attending outdoor high school graduation ceremonies in a northern New Jersey city on Monday were treated for heat exhaustion and related problems, including 16 taken to hospitals. The Paterson school district held ceremonies in the morning and the afternoon as temperatures soared to nearly 100 degrees. Officials halted the second ceremony about an hour after it had started due to the heat.

And in New Hampshire, two 16-year-old hikers were rescued from a mountain in Jaffrey late Monday afternoon, overcome by the heat, the New Hampshire Fish and Game Department said.

The heat hit New York City as residents headed to the polls for the city’s primary election. In the Queens neighborhood of Jackson Heights, Rekha Malhotra was handing out flyers in support of Democratic mayoral candidate Zohran Mamdani while wearing a pink electric fan around their neck.